510 the main alteration domains, confirming the estimated values and improving confidence in the model inputs. The results (Table 1) demonstrate the increased ore hardness compared to the values used for design, and thus the capacity limitations of the comminution circuits due to treating this harder material. Table 4 – Summary of Breakage Test Results Test Unit Design 2014 Samples 2019 Survey 2022 Geomet Testwork Bond Ball Work Index BWi (kWh/t) 12.9 13.3 14.3 13.2 14.2 14.2 SAG Power Index SPI (minutes) 75 129 120 99 - - Drop Weight Index DWi (kW/m3) 6.2* 8.9* 8.5* 7.5* 7.3* 7.0 *Estimated from Hatch in-house relationships. ROM fragmentation is a critical upstream variable influencing SAG mill performance. Optimizing the blast intensity based on ore characteristics (structure and strength) and adjusting crusher gap accordingly, can achieve a finer SAG mill feed and subsequently allow optimization of grinding circuit throughput. This optimization approach has been successfully applied in many operations through mine-to-process optimization projects (Valery et al., 2019) and can be particularly effective when facing hard or highly variable feed ore characteristics. 2.3 Plant Audits and Surveys The downstream comminution and flotation circuits were then optimized, leveraging the benefits of finer ROM fragmentation from drill and blast optimization. This was conducted in phases as the second grinding line (Phase II) did not commence operations until May 2020. The modelling, simulation and optimization of Phase I grinding circuit was conducted in 2020 using historical operating data and results from surveys conducted previously by Chinalco on the 14th and 22nd of September 2019. A full audit and survey supervised by Hatch was conducted in May 2023 for the optimization of the Phase II grinding circuit and the Cu bulk flotation circuit. The audit and survey conducted in May 2023 also included measurement of blast fragmentation and additional rock characterization for the surveyed ores (Figure 2). This allowed comminution performance to be calibrated and linked with ore characteristics and blast fragmentation results. Figure 26 – Audit and Measurement of ROM Fragmentation (May 2023) As part of the survey, crash-stops and grind-outs were also carried out in the SAG and ball mills to gather key information to calibrate the comminution models. the condition of the lifters/liners and ball size distributions were reviewed. In the SAG mill, the extent of pegging and peening of the grates, the capacity
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